Skipper, I see you have the Social Profilr plugin for Wordpress. They have their own icons. If you want to use different icons, best to deactivate this plugin, remove their widget and use a text widget instead.
First--find the icons you want. Leigha gave you some good resources above. Look for icons that are about 50x50px or so.
Next--Upload the image files to your server. You can either FTP them into an images folder or upload them through the Media Library in your Wordpress dashboard. Whichever way you choose, make note of the location or url of each image file in Notepad or some other text editor.
Next--Copy into Notepad all your links to the social sites you have icons for (Twitter, Facebook, LinkedIn, You Tube, etc)
Next--Go to your widgets page and move a text widget into your sidebar.
Next--Insert the html code to build the widget. Here's a sample of that code using Twitter in the example. You will want to insert your links where the all caps words are:
<p align="center">
<a href="http://twitter.com/YOURTWITTERNAME" title="Twitter"
target="_blank" rel="nofollow"> <img src="IMAGEURL"
alt="Twitter"></a>
REPEAT FOR OTHER ICONS
</p>
Looks like you can accommodate a widget that will span 300-330px in your sidebar.